Host-Guest Interactions in the C₅₉N^•⊂[10]CPP Supramolecular Radical

Area of Science:

• Supramolecular chemistry
• Organic radical chemistry
• Nanomaterials science

Background:

• Azafullerene radicals encapsulated in [10]cycloparaphenylene ([10]CPP) nanorings exhibit remarkable stability.
• Understanding the host-guest interactions in these supramolecular complexes is crucial for their application.

Purpose of the Study:

• To investigate the host-guest interaction in C59N•⊂[10]CPP supramolecular complexes.
• To elucidate the structural and electronic properties governing the stability of these radical systems.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy, including continuous wave (CW) and electron spin echo envelope modulation (ESEEM) techniques.
• Density functional theory (DFT) calculations for theoretical support and structural optimization.

Main Results:

• EPR spectra confirmed the presence of monomeric and oligomeric azafullerene radical species within the [10]CPP host.
• ESEEM measurements determined experimental hyperfine coupling constants for 13C, 1H, and 14N atoms.
• Experimental hyperfine couplings agreed well with DFT-calculated values for optimized supramolecular structures.

Conclusions:

• The study demonstrates a weak but non-negligible spin delocalization from the azafullerene guest to the [10]CPP host.
• This spin delocalization explains the observed stability of the supramolecular radical complex.
• Combined EPR and DFT approaches provide valuable insights into radical host-guest structures.